This online lecture provides information about life in extreme environments from the perspective of an undergraduate geology class. It explores current conditions for life, the origins of life, and contemporary harsh environments- particularly the ocean floor. A few extremophiles are introduced: thermophiles, psychrophiles, acidophiles, alkaliphiles, and halophiles. The possibility of life on other planets is examined by highlighting Mars, Europa, Enceladus, Titan, Io, Jovian planets, comets, and meteorites. Images and links to related websites and publications are included.